This is an optional Team Associated 12mm Big Bore Rear Soft Spring Kit, and is intended for use with the Team Associated B4.1, B44.1, T4.1, SC10 and SC10GT 1/10 scale vehicles equipped with the optional Team Associated 12mm Big Bore Shocks. These springs have more coils for a given spring rate which improves the rate tolerances. The springs are also black oxide coated to reduce corrosion without affecting rate tolerances.